The U.S. Patent Application Publication No. US2011/0150487, assigned to the same assignee as the present application, discloses an optical interconnect for high speed optical communication. As described in the Publication, the disclosed interconnect has application for use in establishing a communication link between a first location and a second location, the first location having an electrical driver circuit that receives input data to be communicated, and the second location having an electrical receiver circuit for producing output data representative of the input data. The method includes the following steps: providing a tilted charge light emitting device at the first location and coupled with the driver circuit such that the light produced by the tilted charge light-emitting device is a function of the input data; providing an optical fiber between the first and second locations; coupling light from the tilted charge light emitting device into the optical fiber; and providing, at the second location, a photodetector coupled with the optical fiber and with the receiver circuit; whereby electrical signals representative of the input data are output from the receiver circuit.
At the receiver circuit of such an optical interconnect system, it is necessary to couple the optical signal from the output end of an optical fiber cable into an optical detector, typically a semiconductor photodetector, that converts the optical signal into an electrical signal. It is, of course, advantageous to perform this coupling with high efficiency; that is, with minimal loss of the light leaving the output end of the optical fiber. A problem in the art, however, is that achievement of high efficiency coupling can substantially increase the cost of the receiver subassembly, which is unacceptable when striving to achieve a relatively inexpensive optical interconnect that is suitable for widespread use in communication applications.
There are a number of cost components involved when attempting to implement an efficient optical coupling technique. Initially, it can be noted that the relative sizes (typically diameters) of the optical fiber and the photodetector active area may not be well matched and may vary for different types of optical interconnects. One such cost component is the cost of the optical coupling element itself, for example a lens for focusing light output from the fiber into the photodetector active region. Another component of cost relates to the assembly process, including positioning, aligning, and securing the optical coupling component in place, and doing so without compromising the ultimate optical coupling efficiency of the assembly.
Examples of prior art approaches are shown in FIGS. 1 and 2. Both of these Figures show a receptacle 120 in which is mounted the output end of an optical fiber comprising a core 105 and cladding 108. A lens element 190 focuses light output from the fiber onto a photodetector. In FIG. 1, the light is focused on the backside of a photodetector 180 on a substrate 182. In FIG. 2, the light is focused on the frontside of a photodetector 183 on substrate 182. (The photodetector electrical output is not separately shown.) As illustrated, the prior art can involve the use of relatively large lens or lenses in order to couple light emitted from a fiber onto a photodetector. The lenses are usually constructed of plastic with an index of refraction similar to that of the fiber. Precision is required during assembly to match the separation of the device and the focal length of the lens. Furthermore, the difficulty of constructing a precise curved surface contributes to higher cost of the lenses.
It is among the objects of the present invention to address the drawbacks and limitations of prior art approaches, as described.